1. Technical Field
The present invention relates to a reflow furnace in which a printed circuit board mounting electronic components is soldered, in particular a reflow furnace including an ambient gas purification equipment in which the flux component vaporized during soldering and mixed in the ambient gas is effectively burn-treated.
2. Related Arts
Various electronic components are called as SMDs (Surface Mounted Devices), and are directly mounted on a surface of a printed circuit board and soldered. The soldering is performed with the use of a soldering paste. A cream flux and a particle solder are made paste to prepare the soldering paste. The soldering paste is applied to a portion to be soldered in the printed circuit board by printing, dispenser or the like, and then the electronic components are mounted thereon. The printed circuit board mounting electronic components with the soldering paste is then heated the reflow furnace to melt the soldering paste, thus soldering electronic components to the printed circuit board.
The flux in the soldering paste functions to remove an oxidized film on the metal surface to be soldered, to prevent the metal surface from being re-oxidized by heating during soldering, and to make small the surface tension of the soldering to improve wettability. Since the flux is made by melting the solid elements of pine resin, thixotropic agent, activator or the like with the use of solvent, those are vaporized when the soldering paste is heated and melted in the reflow furnace. The vaporized flux component contacts with a low temperature (up to about 110 Celsius degree) portion of the reflow furnace to be liquidated and attached onto the printed circuit board, thus deteriorating the solder, or thwarting the motion of the movable parts in the reflow furnace.
In order not to deteriorate the solder by the flux component attached onto the printed circuit board, there is proposed a flux collecting equipment in which the ambient gas including an inert gas is heated, and the flux component mixed in the ambient gas is cooled to be liquefied and collected.
The above described conventional collecting equipment is shown in FIG. 4. Electronic components are mounted the printed circuit board 10 which is carried (in a direction vertical to the surface of the drawing) in the heating chamber 103 of the reflow furnace 101 by a carrier device 105. The fan motor 109 is arranged in the upper portion of the carrier device 105. The ambient gas 113 is caused by the fan 111 driven by the motor 109 to pass through the heaters 115 and to be blown onto the carried printed circuit board, thus heated and circulated. A by-pass route 117 is arranged to by-pass the above described circulation of the ambient gas, and the heat sink 119 which is one of the heat exchanger is arranged inside of the by-pass route 117. The ambient gas 113 guided through the by-pass route 117 is cooled by the heat exchange to the outside air, thus the flux component in the ambient gas 113 is liquefied. The flux liquefied on the surface of the heat sink 119 falls in drops into the tank 121 by gravity and is collected therein arranged below the heat sink 119. The ambient gas 123 with the liquefied flux removed is returned to the heating chamber 103.
The ambient gas may be suctioned by the fan separately installed and guided into the by-pass route 117.
There is proposed an ambient gas purification equipment in which the flux gas in the soldering ambient within the soldering equipment body is oxidized by the oxygen catalyst. Refer to Japanese Patent No. 3511396.
In the above described conventional technology in which the flux is liquefied and removed, since the ambient gas 123 returned to the heating chamber is already cooled by the heat sink 119, the remaining flux component not removed in the ambient gas is liquefied at the wall surface with a low temperature, and stuck thereto.
Furthermore, the circulating ambient gas 113 is cooled by the heat sink 119, thus it is necessary to reheat the ambient gas to a required temperature. Accordingly, the consumption power of the heater becomes large, which reverses the energy conservation.
In the conventional technology in which the flux gas is oxidized, since the flux is positively oxidized and decomposed by heating the ambient gas using inflammable materials, the temperature of the gas after the treatment becomes higher, it is necessary to have an additional treatment such as the cooling of the high temperature gas or the like, thus causing an energy loss.